Identify the type of friction: static, kinetic, or rolling
Use the normal force, (N)
Apply the friction formula: (F_f = mu N)
Use (mu_s) for maximum static friction: (F_{s,max} = mu_s N)
Use (mu_k) for kinetic friction: (F_k = mu_k N)
Find the normal force from the situation
For a horizontal surface, use (N = mg) if no other vertical forces act
For an inclined surface, use (N = mg costheta)
Multiply the coefficient of friction by the normal force
Compare applied force with maximum static friction to determine if motion starts
Use the friction force opposite the direction of motion or attempted motion